At issue: Is MRSA testing and prophylaxis a worthwhile approach?

TAKE HOME:

Although infections caused by methicillin-resistant Staphylococcus aureus (MRSA) are a prominent concern for cataract surgeons, leading ophthalmologists discuss the pros and cons of performing universal MRSA screening to guide targeted prophylaxis.

Dr. McDonnell

By Cheryl Gutttman Krader; Reviewed by Peter J. McDonnell, MD, and Stephen D. McLeod, MD

Given the increase in prevalence of methicillin-resistant Staphylococcus aureus (MRSA) colonization and in levels of MRSA antimicrobial resistance, the question arises whether preoperative testing for MRSA to guide targeted prophylaxis should be done routinely in patients undergoing cataract surgery.

Two leading ophthalmologists-Peter J. McDonnell, MD, William Holland Wilmer Professor and director, Wilmer Eye Institute, Johns Hopkins University School of Medicine, Baltimore, and Stephen D. McLeod, MD, Theresa M. and Wayne M. Caygill, MD Endowed Chair and professor, Department of Ophthalmology, University of California–San Francisco-agreed universal testing is not cost-effective.

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Both physicians also concluded that available evidence does not support a selective testing approach in which patients would be screened based on certain history factors.

Speaking in favor of MRSA testing and targeted prophylaxis, Dr. McLeod suggested that selective empiric prophylaxis, i.e., use of intracameral vancomycin (rather than intracameral cefuroxime) in certain individuals considered to be at particularly high risk for MRSA colonization based on history (previous history of colonization or residence in an extended-care facility) might be reasonable considering the effectiveness and relative safety of intracameral vacomycin.

Taking the opponent’s position, Dr. McDonnell underscored the current low rates of postoperative endophthalmitis, the potential for topical antibiotic delivery to achieve target site concentrations exceeding MRSA minimum inhibitory concentrations, and the activity of host defense mechanisms in addition to the lack of adequate criteria for identifying carriers of methicillin-resistant organisms. Based on those considerations, Dr. McDonnell advocated for a universal precautions approach in which every patient should be considered as a potential carrier of MRSA and treated using povidone-iodine lid scrubs, topical antibiotic drops, and draping to isolate the lashes.

Limitations of universal screening

Dr. McLeod

In reviewing the relevant evidence, Dr. McLeod first cited experience from the United Kingdom where implementation of universal screening for MRSA resulted in numerous cases of cataract surgery being withheld.

He said that in 2006, the U.K. Department of Health recommended that all elective surgical admissions undergo screening for MRSA and that anyone testing positive should be treated with a decolonization regimen.

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The treatment for cataract surgery patients involved nasal mupirocin and chlorhexidine baths, but it was not always effective in eradicating MRSA carriage, and in that situation, surgery was not performed, Dr. McLeod explained.

Dr. McLeod discussed the cost effectiveness of universal MRSA screening to guide targeted prophylaxis based on a model published by Sharifi et al. [Ophthalmology. 2009;10:1887-1896]. Assuming a Medicare reimbursement rate of $68 for preoperative MRSA testing, the researchers concluded that a change in prophylaxis indicated by testing would have to reduce infection rates by an order of 10 to be cost effect.

“However, all staphylococcal organisms constitute only about 50% of cases of culture-positive endophthalmitis cases postcataract surgery,” Dr. McLeod said. “So, even if the screening and modified prophylaxis were 100% effective for all staphylococcal species, infection rates could not be reduced by more than half.”

Dr. McDonnell presented calculations on the costs of universal testing that were based on the following values:

·      Annual number of cataract operations = 3 million

·      Endophthalmitis rate = 1 in 3000

·      Proportion of infections caused by methicillin-resistant Staphylococcus = 50%

He also assumed a cost of $100 for preoperative culture and sensitivity testing of specimens from the lid margin and conjunctiva ($300 million total), a 40% positivity rate (1.2 million positive cultures), a cost of $100 for a 10- to 14-day course of antibiotic therapy for culture-positive patients ($120 million), and a $150 charge for a return office visit with culture to confirm efficacy of the decolonization regimen ($180 million).

Based on those figures, Dr. McDonnell said the universal screening and pre-treatment protocol would result in $600 million in additional expenditures.

“Assuming it is 100% effective (which would be an overestimate), it would eliminate 500 infections per year, translating into a cost of $1.2 million per infection,” he said.

Selective screening

Both Drs. McLeod and McDonnell pointed to the absence of specific and sensitive criteria for guiding selective preoperative screening for MRSA carrier status. Citing a study from London involving patients seen in a hospital emergency department, about 60% of the patients would be screened as potential MRSA carriers and 15% of those actually positive would be missed using selection criteria of hospital admission within the past year, previous MRSA colonization, or residence in a care home, Dr. McLeod said.

“Selective criteria would likely be less broad in the general cataract population, but still would be inadequately sensitive and specific,” he said. “Therefore, selective testing and targeted prophylaxis should not be considered.”

Dr. McDonnell cited results from a multicenter study by Olson et al. that showed only older age predicted increased likelihood of having a preoperative eyelid or conjunctival culture positive for methicillin-resistant S. epidermidis (MRSE) or MRSA [Clin Ophthalmol. 2010;(4):1505-1514]. In that study enrolling 399 patients who were at least 50 years old, S. epidermidis (63%) and S. aureus (14%) were the most frequently isolated organisms, and about 40% of patients were positive for either MRSE or MRSA. Multivariate logistic regression analysis did not identify major risk factors other than age, and being a health-care worker or family member of a healthcare worker was specifically not a risk factor for colonization with methicillin-resistant organisms.

Intracameral antibiotic issues

As another possible scenario, Dr. McLeod also discussed use of universal empiric prophylaxis in which vancomycin-not cefuroxime or moxifloxacin-would be used routinely as the intracameral antibiotic. However, he recommended against that approach considering its potential to promote bacterial resistance to vancomycin.

Addressing intracameral antibiotic use for endophthalmitis prophylaxis, Dr. McDonnell said that he suspects this practice will become increasingly prevalent in the United States considering the evidence from European studies demonstrating it reduces the likelihood of endophthalmitis.

“However, to the best of my understanding, the data show prophylaxis with an intracameral antibiotic reduces infection in all patients, not just MRSA carriers,” he said. “Therefore, I still believe that a universal precautions type of approach to preventing MRSA endophthalmitis is probably the most cost effective.”

Peter J. McDonnell, MD

E: pmcdonn1@jhmi.edu

Dr. McDonnell is a board member of Allergan Inc.

Stephen D. McLeod, MD

E: mcleods@vision.ucsf.edu

Dr. McLeod has no relevant financial interests to disclose.

Dr. McDonnell and Dr. McLeod presented these viewpoints in a session during Cornea Day at the 2014 meeting of the American Society of Cataract and Refractive Surgery.